It is known in the art relating to diesel engines to provide a high turbulence combustion chamber recess in the piston head for receiving the directly injected fuel charge and promoting mixing thereof with the cylinder air charge prior to ignition and burning. Numerous configurations for combustion chamber recesses in the piston heads of such engines have been utilized or proposed for obtaining various suggested advantages in mixing and combustion performance.
Beginning with the conventional axisymmetric, or circular, combustion bowl recess, variations have been proposed, including reentrant configurations having an overhanging lip of smaller diameter or lateral dimension than the body of the recess below. Other variations have included straight or angle sided square recesses, square reentrant recesses with a circular lip and various cusp-shaped configurations, among others. To applicants' knowledge, these variations have included rectangular lips with circular recesses and circular lips with rectangular recesses. Rectangular recesses with rectangular openings have also been proposed, but these appear to have been limited to straight sided recesses with parallel, or outwardly or inwardly sloping, sides.